In modern applications, the power delivered to the transducers can be high, thus generating a significant amount of heat in the moving voice coil. This heat has various negative effects, one of which is the possible destruction of the moving coil wire insulation, resulting in an electrical short-circuit and ultimate failure of the device. As the insulation of a voice-coil wire is subjected to temperatures higher than its temperature rating, the life of the insulation will be reduced accordingly. This situation can cause the insulation to be damaged to the point of creating a short-circuit failure. By maintaining the temperature on the voice-coil below its rated temperature, the risk of burning the insulation prematurely is eliminated or greatly reduced.
Another negative aspect of heat generation is the deterioration of the magnetic characteristics of the permanent magnets used in the loudspeaker transducers. As a permanent magnet is subjected to temperatures higher than its temperature rating, its ability to maintain its magnetic characteristics is reduced accordingly. In a magnetic circuit, this loss of magnetic characteristics due to high temperatures has a direct reductive effect on the magnetic flux. In a transducer, the reduction of the magnetic flux will cause a loss in transducer efficiency. By maintaining the temperature of the magnet below its rated temperature, the loss of overall efficiency of the transducer due to overheating is eliminated.
To overcome the problems associated with overheated transducers, some manufacturers have attached a heat dissipating radiator on and/or around the magnetic assembly in order to improve the extraction and dissipation of the heat generated in the voice-coil. In these implementations, there is still a problem with heated air stagnating inside the enclosure, which greatly reduces the effect and benefit of this heat dissipating approach.
One heat dissipating technique is described in U.S. Pat. No. 4,757,547 to Thomas J. Danley. Danley discloses use of a blower connected by conduits directly to holes in the base plate of the magnetic assembly below the voice-coil gap to suck air out of the voice coil gap. In Danley, there is no provision for exchanging the heated air inside the enclosure with cooler outside air.
Therefore, need exists for an efficient cooling system in high-powered loudspeakers, and particularly in loudspeakers using vented enclosures where the heated air inside the enclosure can be exchanged with cooler outside air.